There is a need for polymers of 1-olefins which are prepared by living polymerization, since living polymerization is a valuable method of preparing tailored polymers which are not obtainable by other conventional methods.
In EP-A 206 753, Y. Doi et al. discloses the process of living polymerization using a vanadium Ziegler/Natta catalyst at −78° C.
EP-A 1 209 171, EP-A 634 429, U.S. Pat. No. 5,391,629, WO 01/55231 and also J. Amer. Chem. Soc. 2002, 124, 3327-3336, Chem. Letters 2001, 576 and Angew. Chem 2002, 114, 2361, disclose processes which make it possible to increase the polymerization temperature by use of particular catalysts.
WO 98/01455 and WO 98/45339 describe processes for preparing homopolymers and copolymers by means of transition metal compounds which have a donor-acceptor interaction. However, these processes are carried out using catalysts and at temperatures which prevent a living polymerization. In the process described in the prior art, the length of the polymer chains is not easy to control. The formation of sequence-like block copolymers such as isotactic polypropylene (iPP), atactic polypropylene (aPP) or ethylene-propylene-propene-ethylene copolymers (EPM-EP) have also been reported. However, their are no known simple ways of regulating or controlling the block length of these block copolymers, which possibly result from switching between bridged and unbridged donor-acceptor structures, and there is no known way of preparing 2- or 3-block copolymers in a targeted manner.
A disadvantage of the processes described in the prior art is the use of catalysts which require industrially unattractive reaction conditions. One of the main problems is the need for very low polymerization temperatures of from −70° to −50° C. As a result, the polymerization is too slow and the process becomes uneconomical. The degrees of polymerization and thus the final molar masses achieved are unsatisfactory in these processes.
It is therefore an object of the present invention to provide a process for preparing homopolymers, copolymers and/or block copolymers which makes the living polymerization of 1-olefins possible, and which can be used at elevated temperatures and leads to high molar masses in short polymerization times.